1. Field
Circuit packaging.
2. Background
Circuit dies or chips are commonly provided as individual, pre-packaged units. A typical chip has a flat, rectangular body with a front face having contacts for connection to internal circuitry of the chip. An individual chip is typically mounted to a substrate or chip carrier (substrate package or support circuit), that in turn is mounted on a circuit panel such as a printed circuit board.
Multichip modules have been developed in which typically, several chips possibly having related functions are attached to a common circuit panel and protected by a common package. One advantage to this approach is a conservation of space that might ordinarily be wasted by individual chip packages. However, most multichip module designs utilize a single layer of chips positioned side-by-side on a surface of a planar circuit panel. In “flip chip” designs, a face of the chip confronts a face of a circuit panel and contacts on the chip are bonded to the circuit panel by solder balls or other connecting elements. The flip chip design provides a relatively compact arrangement where each chip occupies an area of the circuit panel equal to or slightly larger than the area of the chip face.
In addition to the above packaging technologies, laminate-type packaging systems have been proposed. In the laminate-type packaging system, chips are mounted on film carriers and the film carriers are laminated on a substrate and connected. For example, a chip may be mounted on a generally flexible tape and the tape is laminated to a circuit panel. Flexible substrate packages such as described above typically have a single metal layer to provide signals to and/or from the chip to the panel. The single metal layer routes to contact structures on the surface of the substrate suitable for connecting to the panel.
Flexible substrates that may contain multiple chips have also been proposed. In this configuration, a chip is mounted to a first portion of a flexible substrate (e.g., tape) and one or more additional chips are mounted at other portion(s) of the flexible substrate. The flexible substrate may then be folded so that the chips mounted to the flexible substrate may be aligned in a superposed or stacked arrangement.
Performance evaluations of a package (e.g., chip and substrate) are used to characterize and classify the capability (e.g., frequency capabilities) of the package. As signal frequency is increased, the contribution of the substrate plays a larger role. For example, critical input/output (I/O) and clock/strobe traces need controlled trace impedance for signal integrity. One way to control trace impedance is to use a ground plane on the substrate. Typically, a ground plane is a blanket layer of a metal material across a face of a substrate. With a foldable substrate, a blanket ground plane can affect foldability.